Steel is made by melting and refining steel scrap in an electric arc furnace (EAF). Today, the EAF is considered by those skilled in the art of steel production to be the single most critical apparatus in a steel mill or foundry. Consequently, it is of vital importance that the EAF remain operational for as long as possible.
Structural damage caused during the charging process is a persistent problem that affects the operation of an EAF. Because scrap has a lower density than molten steel, the EAF must have sufficient volume to accommodate the scrap and still produce the desired amount of steel. As the steel melts it forms a hearth or smelting area in the lower portion of the furnace. As the volume of steel in the furnace is reduced, however, the free volume in the EAF increases. The portion of the furnace above the hearth or smelting area must be protected against the high internal temperatures of the furnace. The vessel wall, cover or roof and duct work are particularly at risk from massive thermal, chemical, and mechanical stresses caused by charging the steel. Such stresses greatly limit the operational life of the furnace.
Historically, the EAF was generally designed and fabricated as a welded steel structure which was protected against the high temperatures of the furnace by a refractory lining. In the late 1970's and early 1980's, the steel industry began to combat such stresses by replacing expensive refractory brick with water-cooled roof panels and water-cooled sidewall panels located in portions of the furnace vessel above the smelting area. Water-cooled panels have also been used to line furnace duct work. Existing water-cooled panels are made both with various grades and types of plates and pipes.
Using water-cooled panels has reduced refractory costs and has also enabled steel makers to operate each furnace for a greater number of heats. Furthermore, water-cooled equipment has enabled the furnaces to operate at increased levels of power. Consequently, production has increased and furnace availability has become increasingly more important.
Although water-cooled panels last longer than the brick refractory they replaced, the panels have serious problems with wear and are subject to damage. It is now common in the steel making industry to expect a critical breakdown of one or more of the panels within a few months of the furnace going on line.
When a water-cooled panel is damaged and water begins to leak into the interior chamber of the EAF, serious operational issues are encountered. When such a breakdown occurs, the damaged water-cooled panels must be replaced as soon as possible. To make this repair, the EAF must be taken out of production for unscheduled maintenance. This unscheduled downtime can have serious repercussions throughout the steel mill. For example, when the furnace is down, no molten steel is being produced by the steel mill which can cost as much as five thousand dollars per minute for the production of certain types of steel. Such interruptions also decrease production and significantly increase operating expenses. Also, making unscheduled repairs to the furnace panels constitutes a considerable percentage of maintenance expenses.
A need, therefore, exists for an improved water-cooled furnace panel that can remain operable longer than existing comparable panels and that can remain operable, despite some structural damage, until scheduled maintenance occurs.